The present invention relates to a plasma display device and method of making the same, and, more particularly, to a plasma display in which the back panel is formed by laminating layers of dielectric material to a metal core, placing metal electrodes on or between the dielectric layers and embossing the laminated layers to form ribs on the back panel.
A typical plasma display includes a front panel and a back panel both made of sheet glass (e.g. conventional float-glass). Electrical connections and mechanical structures are formed on one of both of the panels. For example, the back panel may have a ribbed structure formed on it such that the space between the ribs defines a pixel in a direct current (DC) display or column of pixels in an alternating current (AC) display. The ribs prevent optical cross-talk, that is to say, light from one pixel leaking into an adjacent pixel. Fabrication of these ribbed structures, called barrier ribs, poses a challenge both in the materials and manufacturing techniques that are used.
Plasma displays operate by selectively exciting an array of glow discharges in a confined rarefied noble gas. Full color displays are made by generating a glow discharge in a mixture of gases, such as Hexe2x80x94Xe or Nexe2x80x94Xe gas mixture to produce ultraviolet light. The ultraviolet light excites phosphors in the pixel cell, as defined by the barrier ribs, to produce light of desired color at the pixel position.
A typical plasma display back panel comprises a glass substrate having a plurality of substantially parallel, spaced first electrodes on a surface thereof. In AC displays, a thin layer of a dielectric material, such as a glass, typically covers the electrodes. Barrier ribs are formed on the surface of the glass substrate between the first electrodes. The barrier ribs project from the surface of the substrate at a distance greater than the thickness of the first electrodes. Red, green and blue (R-G-B) phosphor layers overlie alternating columns of the first electrodes in the spaces between the barriers and also overlie the walls of the barriers. A front transparent glass substrate, the front panel, overlies the rear panel and may rest on the barrier ribs so as to be spaced from the rear glass substrate by the barrier ribs.
Typically, the barrier ribs are walls which define troughs or channels on the back panel. Alternating current (AC) plasma displays typically have barriers that form the separators for the column pixels, and hence. have continuous vertical ribs on the back plate. By contrast, direct current (DC) plasma displays typically have ribbed barriers which isolate each pixel from all of its neighbors. Thus, for DC displays, the rib structure has a rectangular lattice-like layout. In either case, the desired resolution for the display device and its size determine the size of the ribbed barriers. In a typical display, the ribs are 0.1 to 0.2 mm in height, 0.03 to 0.2 mm wide and on a 0.1 to 1.0 mm pitch. For example, a barrier pitch of about 211 xcexcm is desirable for the back panel of a 55 inch diagonal high-definition television (HDTV) display and a barrier height of about 161 xcexcm is desirable for the back panel of a 42 inch diagonal HDTV display. These barrier ribs desirably have a height of less than 200 xcexcm and a width of less than 60 xcexcm.
Barrier ribs for plasma display devices having lower resolution may be formed separately from the back plate and attached using an adhesive or, as set forth in U.S. Pat. No. 5,674,634, entitled xe2x80x9cINSULATOR COMPOSITION, GREEN TAPE, AND METHOD FOR FORMING PLASMA DISPLAY APPARATUS BARRIER RIBxe2x80x9d to Wang et al. The barriers may also be formed on the back plate by laminating a ceramic green tape to a ceramic or glass back plate, sandblasting the green tape to form the channels between the barriers and then firing the back plate in a kiln to convert the green tape barriers into ceramic barriers.
Plasma display panels having lower resolution may also be formed by embossing a green ceramic tape as set forth in U.S. Pat. No. 5,747,931 entitled xe2x80x9cPLASMA DISPLAY AND METHOD OF MAKING SAMExe2x80x9d to Riddle et al. The plasma displays described in this patent are formed by embossing a laminated green ceramic tape and then bonding the embossed tape to a metal substrate.
The front panel of a plasma display device typically includes an array of substantially parallel, spaced second electrodes on its inner surface. These second electrodes extend substantially orthogonally to the first electrodes. A layer of a dielectric material, typically glass, covers the second electrodes. A layer of MgO covers the dielectric layer. Voltages applied to the electrodes in the proper manner excite, maintain and extinguish a plasma in the as within the region formed by the barriers. Addressing of individual pixels is done using external circuitry at the periphery of the panel. Barrier structures are typically used to confine the discharge to the addressed pixel, eliminating both electrical and optical cross talk between adjacent pixel elements. The columns of pixels are separated by the barriers, and the first electrodes are arranged beneath the gaps between the barriers. In a DC plasma display, the electrodes are not covered with glass or MgO, and the barrier structures are typically crossed, providing a box-like structure at each pixel element.
Although the structure and methods described above may be suitable for a low resolution plasma display they cannot easily be used to produce a high resolution display such as for a 42 inch or 55 inch HDTV display.
The present invention is embodied in a plasma display device of the type having a composite back plate including a metal substrate and a ceramic barrier rib structure, wherein the materials used to form the back plate have compatible thermal coefficients of expansion.
According to one aspect of the invention, the ceramic structure is formed using a green ceramic tape which is a combination of two glasses, a primary glass which flows back during firing and a secondary glass that has a relatively high thermal coefficient of expansion.
According to another aspect of the invention, channels are formed on the inner surface of the back panel by laminating a green ceramic tape to the metal substrate and then soaking the laminated tape in a solvent before embossing the green tape to form the ribs.
According to yet another aspect of the invention, the ceramic components of the green tape are formulated with a particle size 15 xcexcm or more to enhance particle flow when the green tape is embossed.
According to another aspect of the invention, electrodes are printed onto one or more of the green ceramic tape layers, by screen printing using a metal emulsion screen, prior to embossing such that the electrode layer covers all or substantially all of the green tape layer and the electrodes are separated by the embossing process.
According to yet another aspect of the invention, the electrodes are printed onto one or more of the green ceramic tape layers using a conductive ink which may be applied using an inkjet printing technique.
According to yet another aspect of the invention, the electrodes are formed from sheets of conductive material and applied to the back panel either before or after the panel is embossed.